Review: remove markup function aliasing mechanism (was: Half-baked unused features.)

[David Kastrup]

The aliasing functionality is unused in the current source code, not
documented at user level, and not sure to be fully working (there are no
regtests to check).  Documenting it complicates the documentation
without an immediately visible user benefit.

The patch likely does not apply to a pristine source, but I checked that
it still passes the regtests.

<URL:http://codereview.appspot.com/1995042>

-- 
David Kastrup